Layer up.

During rides that involve low temperatures, your base layer acts as an insulator for your body. Similarly, in warm weather, that same layer under your jersey works to pull moisture away from your skin in order to keep you cool and comfortable. Castelli understands that the inconspicuous under-layer is hard at work regardless of your riding weather, which is why it introduced the Seamless Base Layer.

Castelli's Seamless Base Layer was constructed using two fabrics: polypropylene and nylon. These materials work in tandem in oder to perform the base layer's primary function -- pulling moisture away from the skin and drying it. Accordingly, the inner-layer is comprised of the polypropylene material, as it effectively pulls moisture away from the skin and transfers it to the outer-layer of nylon. And because nylon is lightweight and maintains an airy composition, it's a naturally efficient evaporator. The material dries much quicker than most, which means that instead of simply soaking you in your sweat, the base layer keeps you cooler by evaporating moisture next to the skin.

This moisture transfer is furthered by the three different mesh patterns on the base layer. Taking anatomy into account, this system maintains a consistently open mesh in order to provide the most ventilation possible, which keeps your body dry and comfortable throughout your rides.

The Castelli Seamless Base Layer is available in the sizes Small/medium, Large/x-large, and XX-Large and in the color White.

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Average ride time is based on Strava activity over the last 3 months. Give your reviews credibility by connecting your account.

Might be my favorite piece of kit

Familiarity: I've used it several times

Fit: True to size

I have both this and the other Castelli mesh baselayer, and while they cost about the same amount, this one is head and shoulders above its sibling. The material is much thicker, stretchier, and more substantial. I find this type of mesh baselayer keeps me cool on hot rides and warm under my kit on cold rides, so I wear one on essentially every ride. I also think it takes the brunt of the sweat, and as such I feel like I can wash my jerseys less often, which lets them live a bit longer. All-in-all, this is my concept of the perfect baselayer and I could not recommend it more highly. Other comments are accurate, when you take it out of the box it will look like it was made for a small child...trust me, it stretches.

Comment on Noel's review:

Great baselayer for warm temps.

Familiarity: I've used it several times

Fit: True to size

Size Bought: L/XL

A great base layer for warm to hot days. It is well made and comfortable -- and creates a bit higher layer than the similar mesh base from Castelli. I like how this piece prevents chafing and keeps me cool. It is well made too and holds up in the wash, though I usually use a garment bag to keep it safe.

Comment on Gregory R.'s review:

Average ride time is based on Strava activity over the last 3 months. Give your reviews credibility by connecting your account.

Makes all the difference

Familiarity: I've used it several times

I was skeptical that a baselayer could be used effectively under a jersey in both cold and dry temperatures, and I am so happy that this skepticism was wiped away. This undershirt keeps the jersey off of your skin and wicks away sweat so well that you never get that "wet jersey" feeling on those long hot rides. On the other side, when it's cold outside, it keeps that layer of warm air close to you thanks to the "unique" fishnet design. I will not be riding without this and may buy a second at this price point.

Comment on Ryan S's review:

Buy this

Castelli offers arguably the largest lineup of pro & performance cycling clothing made in the sport. The experience, detail, and 'know-how' that Casteli puts into their gear is pretty amazing. This is seen for example in Castelli's lightness glove, climber's jersey, Mortirolo jacket, and even their cycling socks.

This "seamless" baselayer is designed to be used in -warm- weather. It is made with special moisture transfer fabrics. It is also designed with "open mesh" construction to hold your jersey off your skin. These features promote moisture transfer, sweat evaporation and cooling. It works!

Every serious rider should consider using a baselayer like this in warm weather.

Comment on Jonny Heinken's review:

A micro-climate for your core!

Familiarity: I've used it once or twice and have initial impressions

I'm a big believer in technical undershirts for low temperatures on up to about 80 degrees F. Beyond 80 in a low humidity environment I can't see much benefit over having a good quality jersey against my skin, but there are situations where it could still be helpful. This undershirt is perfect for the temps I've been riding in lately, 45 to 65 degrees. It creates a nice layer of trapped air while efficiently moving moisture away and keeping me dry with a stable core temp. It's very mesh like, and given it's stretch the sizing is very forgiving. It has a nice long torso and lays flat against your skin. It will look very small when you pull it out of the box. My wife laughed when she saw it and insisted I never let anyone see me in it! So of course I made it a point to walk around the house in it! My only complaint is that the material will snag easily. Use caution if you're wearing a watch when you put it on, and perhaps, be willing to accept that you'll get some snags that widen some of the mesh openings over time.

Comment on Eric's review:

Totally Awesome Base Layer!

Familiarity: I've put it through the wringer

Unbelievable fabric & mesh design. Wicks better than any other base I've used in the past. Ideal for hot days too! It keeps a dry (not clammy) layer against your skin thus keeping you comfortable on hot days. Wicks moisture to outer jersey where it evaporates. I love this base. I am 5'7" @ 165lbs. chest 40" and a lg/ex lg. size fits snug like it was designed to fit for maximum efficiency.

Comment on Charles H.'s review:

Average ride time is based on Strava activity over the last 3 months. Give your reviews credibility by connecting your account.

Awesome Base Layer

Familiarity: I've used it once or twice and have initial impressions

This base layer did exactly what I was hoping it would do. It helps me maintain an even body temperature in various Fall climates and keeps my jersey from getting sweaty and cold against my skin. It works well for me in temps from mid 50 degrees to mid 80 degrees, but I have hopes that I can use this base layer year round. Very impressed with the quality as well. I can barely tell it's on when I wear it. One note, when you get first pull it out of the box it will be tiny like a child's shirt. I'm 5'10' 150lbs. and the S/M fits perfect.